This invention relates to a method for the production and treatment of stereoregular propylene polymers and more particularly to the treatment of isotactic propylene polymers involving the incorporation of ethoxylated amines as processing aids.
Thermoplastic olefin polymers, such as linear polyethylene, polypropylene, and olefin copolymers, such as propylene/ethylene copolymer, are conveniently formed in continuous loop-type polymerization reactors and thermoformed to arrive at granules or pellets of the polymers. For example, polypropylene and/or propylene/ethylene copolymers are polymerized in continuous polymerization reactors in which the monomer stream is introduced into a reactor and circulated with an appropriate catalyst to produce the olefin homopolymer or copolymer. The polymer is withdrawn from the catalyst reactor and subjected to appropriate processing steps and then extruded as a thermoplastic mass through an extruder and die mechanism to produce the polymer as a raw material in particulate form, usually as pellets or granules. The polymer particles are ultimately heated and processed in the formation of the desired end products.
Polypropylene and propylene copolymers, as used in various applications involving production of films, fibers, and similar products in the polymers, are thermo-processed and shaped or oriented by one uni-directional or bi-directional stresses. Such polymers are thermoplastic crystalline polymers. Polymers of this nature are subject to degradation due to high temperatures and photochemical action induced by electromagnetic radiation in the visible light range and in the ultraviolet region. In order to retard the degradation of such polymeric objects, the base polymer system, which is molded or extruded to form the desired object, e.g. fiber or film, may be treated with hindered amine light stabilizers, identified by the acronym xe2x80x9cHALS (hindered amine light stabilizers)xe2x80x9d which function to protect the film, fiber, or other object against degradation due to electromagnetic radiation by radiation in the visible light spectrum.
Isotactic polypropylene is conventionally used in the production of films in which the polypropylene is heated and then extruded through one or more dies to produce a film or tape. The film thus produced can then be oriented in at least one direction. Typically, the polypropylene is heated and extruded and then subjected to biaxial orientation by stressing the film in both a longitudinal direction (referred to as the machine direction) and in a transverse or lateral direction sometimes referred to as the xe2x80x9ctenterxe2x80x9d direction. The structure of isotactic polypropylene is characterized in terms of the methyl group attached to the tertiary carbon atoms of the successive propylene monomer units lying on the same side of the main chain of the polymer. That is, the methyl groups are characterized as being all above or below the polymer chain. Isotactic polypropylene can be illustrated by the following chemical formula: 
Stereoregular polymers, such as isotactic and syndiotactic polypropylene, can be characterized in terms of the Fisher projection formula. Using the Fisher projection formula, the stereochemical sequence of isotactic polypropylene, as shown by Formula (2), is described as follows: 
Another way of describing the structure is through the use of NMR. Bovey""s NMR nomenclature for an isotactic pentad is . . . mmmm . . . with each xe2x80x9cmxe2x80x9d representing a xe2x80x9cmesoxe2x80x9d dyad, or successive methyl groups on the same side of the plane of the polymer chain. As is known in the art, any deviation or inversion in the structure of the chain lowers the degree of isotacticity and crystallinity of the polymer.
In contrast to the isotactic structure, syndiotactic propylene polymers are those in which the methyl groups attached to the tertiary carbon atoms of successive monomeric units in the polymer chain lie on alternate sides of the plane of the polymer. Using the Fisher projection formula, the structure of syndiotactic polypropylene can be shown as follows: 
The corresponding syndiotactic pentad is rrrr with each r representing a racemic diad. Syndiotactic polymers are semi-crystalline and, like the isotactic polymers, are insoluble in xylene. This crystallinity distinguishes both syndiotactic and isotactic polymers from an atactic polymer, which is non-crystalline and highly soluble in xylene. An atactic polymer exhibits no regular order of repeating unit configurations in the polymer chain and forms essentially a waxy product. Catalysts that produce syndiotactic polypropylene are disclosed in U.S. Pat. No. 4,892,851. As disclosed there, the syndiospecific metallocene catalysts are characterized as bridged structures in which one Cp group is sterically different from the others. Specifically disclosed in the ""851 patent as a syndiospecific metallocene is isopropylidene(cyclopentadienyl-1-fluorenyl) zirconium dichloride.
In most cases, the preferred polymer configuration will be a predominantly isotactic or syndiotactic polymer with very little atactic polymer. Catalysts that produce isotactic polyolefins can be characterized as falling in two general classes, metallocene catalysts and so-called xe2x80x9cconventionalxe2x80x9d Ziegler-Natta catalysts. The conventional Ziegler-Natta catalysts are stereospecific complexes formed from a transition metal halide and a metal alkyl or hydride. Metallocene catalysts are coordination compounds or cyclopentadienyl groups coordinated with transitional metals through xcfx80 bonding.
The polymerization catalysts may be characterized as supported catalysts or as unsupported catalysts, sometimes referred to as homogeneous catalysts. Metallocene catalysts are often employed as unsupported or homogeneous catalysts, although, as described below, they also may be employed in supported catalyst components. Traditional supported catalysts are the so-called xe2x80x9cconventionalxe2x80x9d Ziegler-Natta catalysts, such as titanium tetrachloride supported on an active magnesium dichloride, as disclosed, for example, in U.S. Pat. Nos. 4,298,718 and 4,544,717, both to Myar et al. A supported catalyst component, as disclosed in the Myar ""718 patent, includes titanium tetrachloride supported on an xe2x80x9cactivexe2x80x9d anhydrous magnesium dihalide, such as magnesium dichloride or magnesium dibromide. The supported catalyst component in Myar ""718 is employed in conjunction with a co-catalyst such and an alkylaluminum compound, for example, triethylaluminum (TEAL). The Myar ""717 patent discloses a similar compound which may also incorporate an electron donor compound which may take the form of various amines, phosphenes, esters, aldehydes, and alcohols.
Stereospecific metallocenes are disclosed in U.S. Pat. Nos. 4,794,096 and 4,975,403, both to Ewen. These patents disclose chiral, stereorigid metallocene catalysts that polymerize olefins to form isotactic polymers and are especially useful in the polymerization of highly isotactic polypropylene. As disclosed, for example, in the aforementioned U.S. Pat. No. 4,794,096, stereorigidity in a metallocene ligand is imparted by means of a structural bridge extending between cyclopentadienyl groups. Specifically disclosed in this patent are stereoregular hafnium metallocenes which may be characterized by the following formula:
xe2x80x83Rxe2x80x3(C5(Rxe2x80x2)4)2HfQpxe2x80x83xe2x80x83(4)
In Formula (4), (C5(Rxe2x80x2)4) is a cyclopentadienyl or substituted cyclopentadienyl group, Rxe2x80x2 is independently hydrogen or a hydrocarbyl radical having 1-20 carbon atoms, and Rxe2x80x3 is a structural bridge extending between the cyclopentadienyl rings. Q is a halogen or a hydrocarbon radical, such as an alkyl, aryl, alkenyl, alkylaryl, or arylalkyl, having 1-20 carbon atoms and p is 2.
Metallocene catalysts, such as those described above, can be used either as so-called xe2x80x9cneutral metallocenesxe2x80x9d in which case an alumoxane, such as methylalumoxane, is used as a co-catalyst, or they can be employed as so-called xe2x80x9ccationic metallocenesxe2x80x9d which incorporate a stable non-coordinating anion and normally do not require the use of an alumoxane. For example, syndiospecific cationic metallocenes are disclosed in U.S. Pat. No. 5,243,002 to Razavi. As disclosed there, the metallocene cation is characterized by the cationic metallocene ligand having sterically dissimilar ring structures which are joined to a positively-charged coordinating transition metal atom. The metallocene cation is associated with a stable non-coordinating counter-anion. Similar relationships can be established for isospecific metallocenes.
While metallocene catalysts are generally proposed for use as homogeneous catalysts, it is also known in the art to provide supported metallocene catalysts. As disclosed in U.S. Pat. Nos. 4,701,432 and 4,808,561, both to Welborn, a metallocene catalyst component may be employed in the form of a supported catalyst. As described in the Welbom ""432 patent, the support may be any support such as talc, an inorganic oxide, or a resinous support material such as a polyolefin. Specific inorganic oxides include silica and alumina, used alone or in combination with other inorganic oxides such as magnesia, zirconia and the like. Non-metallocene transition metal compounds, such as titanium tetrachloride, are also incorporated into the supported catalyst component. The Welborn ""561 patent discloses a heterogeneous catalyst which is formed by the reaction of a metallocene and an alumoxane in combination with the support material. A catalyst system embodying both a homogeneous metallocene component and a heterogeneous component, which may be a xe2x80x9cconventionalxe2x80x9d supported Ziegler-Natta catalyst, e.g. a supported titanium tetrachloride, is disclosed in U.S. Pat. No. 5,242,876 to Shamshoum et al. Various other catalyst systems involving supported metallocene catalysts are disclosed in U.S. Pat. No. 5,308,811 to Suga et al and U.S. Pat. No. 5,444,134 to Matsumoto.
The polymers normally employed in the preparation of oriented films are normally prepared through the use of conventional Ziegler-Natta catalysts of the type disclosed, for example, in the aforementioned patents to Myar et al. Thus, U.S. Pat. No. 5,573,723 to Peiffer et al discloses a process for producing biaxially-oriented polypropylene film based on an isotactic polypropylene homopolymer or propylene ethylene co-polymers. Other co-polymers of propylene and alpha-olefins having from 4-8 carbon atoms also may be employed in the Peiffer process.
It is also known to produce polypropylene-based films from syndiotactic polypropylene. Thus, syndiotactic polypropylene, such as that produced by syndiospecific metallocenes of the type disclosed in the aforementioned U.S. Pat. No. 4,892,851, can be used to produce oriented polypropylene films. Processes for the preparation of biaxially-oriented polypropylene films employing polymers produced by the use of isospecific metallocenes are disclosed in Canadian Patent Application No. 2,178,104. Isotactic polymers disclosed there are based upon the polymerization of propylene in the presence of heavily substituted silicon-bridged bis(indenyl) ligand structures involving di- or tri-substituted indenyl groups. The various polymers produced by these metallocenes catalysts are characterized in terms of molecular weight, molecular weight distribution, melting point, meltflow index, mean isotactic block length, and isotactic index as defined in terms of mm triads. The polymers produced had isotactic indices, as thus defined, of about 97-98% as contrasted with an isotactic index of 93% for a commercial polypropylene compared with a conventional Ziegler-Natta catalyst and molecular weight distributions ranging from about 2.0 to 3.0 as contrasted with a molecular weight distribution of 4.5 for the polypropylene produced by the conventional Ziegler-Natta catalyst.
In employing polypropylene and other polyolefin polymers, there are large numbers of additives which are sometimes used. As noted previously, hindered amine light stabilizers can be used. Other stabilizers which can be employed to stabilize the polymer product and the products into which the polymers are incorporated include various additives which function to stabilize the polymer products, not only against light or UV degeneration but also against thermal or oxidative degeneration or actinic degradation. Thus, as disclosed in U.S. Pat. No. 4,325,863 to Hinsken et al, various benzofuranone or indolinone compounds can be used as stabilizing agents for such polymers as polypropylene, polyethylene, propylene ethylene co-polymers, and various other polymeric materials. As disclosed in Hinsken et al, a wide range of benzofuranones, which may be substituted or unsubstituted to include both polycyclic and monocyclic lactones, can be employed. Preferably, these are incorporated in extruders in which the stabilizing compounds are mixed with granules of such polyethylene or polypropylene granules and then extruded into the desired product. U.S. Pat. No. 5,175,312 to Dubs et al discloses the use of various phenol benzofuran-2-ones as stabilizers in the polymeric materials which are formed into films, fibers, tapes, and the like. The 3-phenol benzofuranones of Dubs et al are generally characterized to include 3-phenol benzofuranones with substituent groups at the 7 position of relatively high molecular weight, e.g. alkyl, containing 14 or more carbon atoms, with substituent groups at either or both of the 4 and 5 positions of alkyl groups or various cyclo-alkyl substituents of somewhat lower molecular weights. The phenol substituent at the 3 position can be substituted with C1-C4 alkoxy, halide, or C1-C8 alkyl groups.
A somewhat different class of additives for use with polyolefins, such as polyethylene and polypropylene, are anti-static additives usually referred to simply as xe2x80x9canti-stats.xe2x80x9d Anti-stats which can be employed in conjunction with polymeric products, including films or molded objects, include medium to high molecular weight polyhydric alcohols, such as glycerol monolaurate or glycerol monostearate and ethoxylated tertiary amines of intermediate to high molecular weight. For example, U.S. Pat. No. 4,314,040 to Castro et al discloses an anti-stat which can be incorporated into a olefinic polymer such as polyethylene. In Castro et al, the anti-stat compositions are prepared by mixing a tertiary amine, such as N,N-bis-(2-hydroxyethyl) alkylamine with polypropylene with the product then suitable for use in polyethylene products. The alkyl groups are of intermediate to high molecular weight, ranging from about C6 to C18. Specifically disclosed in Castro et al is a tertiary amine such as N,N-bis-(2-hydroxyethyl) tallow amine and N,N-bis-(2-hydroxyethyl) coco amine incorporated in an amount within the range of 25-75 wt. % with a polymer such as polypropylene or polystyrene. The tertiary amine polyolefin blend is then added to a polyethylene as an anti-stat composition.
In accordance with the present invention, there is provided a process for the production and treatment of a stereoregular propylene polymer such as specifically isotactic polypropylene. The isotactic polypropylene can be produced by catalysis employing a metallocene catalyst or employing a Ziegler-Natta catalyst. In carrying out the invention a polymerization reactor is operated to provide for the reaction of propylene supplied to the reactor to produce a stereoregular propylene polymer fluff. A product stream containing unreacted propylene and the propylene polymer fluff is withdrawn from the polymerization reactor. The product stream is treated to separate at least a portion of the unreacted propylene from the product stream. The polymer fluff is heated to a temperature sufficient to melt the propylene polymer. A tertiary amine is incorporated into the propylene polymer fluff in an amount within the range of 0.01-0.08 wt. %. The tertiary amine is characterized by the formula: 
wherein R is an aliphatic group containing 8-18 carbon atoms and Rxe2x80x2 and Rxe2x80x3 are each independently a hydroxyalkyl group containing from 1 to 3 carbon atoms. Subsequent to the heating and incorporation of the tertiary amine, the heated polymer fluff containing the tertiary amine is extruded to produce particles of the propylene polymer. In a further aspect of the invention, the resulting propylene polymer particles are heated to a molten state and extruded to produce an initial film. The initial film is processed by drawing of the film at differential speeds to directionally orient the film in the machine direction at a line speed of 300 feet per minute or more. Thereafter, the film is stressed in the transverse direction to provide a biaxially-oriented film.